Base cars had no side mouldings at all. The Custom Exterior package varied between Volare & Aspen, but both included vinyl inserted polished aluminum side mouldings running from the front fenders to the rear quarter panels. Aspen mouldings were placed higher on the body than Volare mouldings. There may have been other parts to the package, but I haven't specifically checked.
When Aspen/Volare were introduced in 1976, the base, mid-level and highline cars all could be identified by their model designations (L, H, P). All L cars had no model name, H cars were Custom for both Aspen & Volare. P were Aspen SE and Volare Premier respectively. In 1977 the model designations went away and ALL cars were identified as "L". The Custom and Premium(SE/Premiere) exterior and interior treatments became packages. So it was possible to get a plain car outside with a Premiere interior, or vice-versa. I personally have seen a number of cars with a Custom exterior and base interior.
